We will continue study on: 1. The lac repressor and the catabolite gene activator protein (CGA protein) of Escherichia coli. 2. th molecular mechanism of action of bromodeoxyuridine (BrdU), a drug that selectively blocks the expression of differentiated functions in mammalian cells. 3. The molecular mechanism of X chromosome inactivation in mammals. 4. Eukaryotic chromosome isolation, separation, and characterization. 5. The biological function of DNA methylation, with the aim of proving the involvement of DNA methylation in gene regulation, and for X inactivation. BIBLIOGRAPHIC REFERENCES: Lin, S. and A.D. Riggs. (1976) The binding of lac repressor and the catabolite gene activator protein to halogen-substituted analogues of poly(d(A-T)). BIOCHIM. BIOPHYSICA ACTA 432:185-191. Lin, S., D. Lin, & A.D. Riggs. Histones bind more tightly to bromodeoxyuridine-substituted DNA than to normal DNA. NUCLEIC ACIDS RESEARCH, (In press, 1976).